This invention relates to improvements in heat engines and turbines. In particular to engines of the rotary or turbine type, operating on a split cycle. The term "split cycle" is used here to denote heat engines in which the various stages of the thermo-dynamic process or cycle to which the working fluid is subjected, are effected in separate chambers, usually compression, combustion and expansion chambers.
Usually in these engines the compression of the air or working fluid does not present any undue problems. But the motor or turbine unit, which contains the expansion chamber, can suffer damage from overheating.
Such heat damage can especially occur where even the slightest clearance is present between the working parts, or working parts and workroom or housing, when hot gases under pressure are to be retained within a certain area. These hot gases can then leak out through such clearances and their heat together with the resultant friction on leaking out through restricted clearances, is such that adjacent areas are seriously damaged.
Other areas, by virtue of the fact that they are in contact with the hot combustion gases, may tend to overheat, and thereby suffer damage.
In the familiar piston engine these problems are overcome by sealing such clearances as may exist, for example between piston and cylinder with piston rings, i.e. seals of sliding contact, thus preventing compressed gases from leaking out of the workchamber.
Areas which may tend to overheat are cooled by a cooling medium, usually air or water and the energy absorbed by this medium is then dissipated to atmosphere. This energy is therefore irretrivably lost.
In the now also familiar gas turbine where sealing with seals of sliding contact is not possible, or practical, it is customary to provide pressurised air of lower temperature to the endangered areas thereby separating the endangered parts from the hot combustion gases. This cooler air is drawn off from the compressor after compression and channeled to the endangered areas. This effect is then often combined with labyrinth seals.
Our present gas turbines are of axial flow or centrifugal flow, and under such non-positive displacement conditions the above method of air-cooling or air sealing does not usually present any problems.
However in more recently invented engines, for example where the motor or turbine unit is of the positive displacement type turbine, such as in Australian Invention No. 487,536, such cooling and sealing is mostly not practical. The motor workroom pressures here are often of considerably higher value than the compressor out-put pressure.
In one of my inventions subsequent to Australian Invention No. 487,536 the engine referred to in the specifications relating thereto can operate in such a fashion that the compressed air from the compressor is transferred to the combustion chamber or burner area by means of a rotary positive dispacement device. In the combustion chamber the pressure of the working fluid is permitted to rise as heat is added by means of combustion of fuel. Because the expansion of the working fluid is to a certain extent restricted during the combustion process the pressure in this area will rise and can be of considerably higher value than the compressor output pressure.
In this case then the pressure of any air drawn off from the compressor output would be insufficient to overcome the pressure of the combustion chamber or of that area.
The hotter gases being of a higher pressure than the cooler gases, would simply displace the cooling air so that effective cooling could not take place.
Sealing means as used in the conventional piston engine are not practical here because of the fast rotational working speed on one hand, and on the other because of the interrelationship of the working parts, especially of interceptor and vane.